Process of and apparatus for lowtemperature separation of air



April 16, 1957 P. K. RICE 2,788,646

PROCESS OF AND APPARATUS FOR LOW-TEMPERATURE SEPARATION OF AIR 2 Sheets-Sheet 1 Filed March 24, 1953 IN! 'EXTOR.

PHILIP K. RICE |...,|II m n H M MM & ww 2 @1 as Q R L k HS M. T %N l g mm m am E... a m? Q o m PROCESS OF AND APPARATUS FGR LOW- TEMPERATURE SEPARATION OF AIR Philip K. Rice, White Plains, N. Y., assignor to Union Carbide and CarhonCorporation, a corporation of New York Thisinvention relates. to an improved process andappa ratus for the low-temperature separation of air to produce oxygen and nitrogen. products, and more particularly to improvements of such process and apparatus resulting in the simplification of, or elimination of, refrigerationproducing equipment, and a reduction of the time and cost of starting an air separation system.

In systems for the low-temperature. rectification of air, especially those for producing large amounts of oxygen, removal of the water vapor and carbon dioxide is more economically effected by refrigeration than by mechanical means, but removal of the impurities, and particularly carbon dioxide, by refrigeration, has necessitated the use of expensive heat exchangers provided in duplicate or regenerative heat exchangers with low initial pressures. If periodically reversed regenerators, as proposed by M. Franklin, for example, United States Patent No. 1,970,299, are employed, refrigeration. requirements of the process necessitate an expansion with the production of external work and the gas which is expanded is most conveniently a portion of the air. Since partly-cooled air would contain carbon dioxide and thus interfere with the expansion process, it has been proposed to employ air that has been cooled to condensation temperature, freed of carbon dioxide, and reheated to the desired temperature, for the efficient expansion with external work. Such reheating employs large heat exchangers that are provided: in duplicate because the air employed for the reheating contains carbon dioxide which is deposited on heat exchanger surfaces. The duplication permits thawing of a clogged heat exchanger without interruption of the operation. An example of such a system is shown and described in United States Patent No. 2,619,810 of Philip E. Rice and Edward F. Yendall. Since such heat exchangers are a large item of equipment, the elimination of at least one of them is an important advantage.

Usually in such systems it is more economical to provide equipment for producing refrigeration (e; g., expansion engine or turbine and heat exchanger) of a size and refrigeration-producing capacity large enough only for the desired steady rate of oxygen production. Therefore the starting of such a system after a shut-down period requires a long initial period of nonproductive operation. The practice of installing extra refrigeration-producing capacity to shorten the starting period adds expensive nonproductive equipment.

Among the objects of the present invention are to pro vide improved process of and apparatus for the lowtemperature separation of air which permits operation to continue during a period when part of the heat exchange and refrigeration-producing devices are shut down for elimination of accumulated carbon dioxide; and which supplements the refrigeration produced by the operating refrigeration-preducing devices so that quiclc starting of the entire apparatus after a long.- period of shut down can be effected without the use of extra mechanical refrigeration capacity.

Customary air separation plants are etficiently operated nited States atenr only at a substantially constant and continuous production rate, but there are occasions where the complete oxygen output of a plant could economically supply a single large consumer, such as a steel mill if the demand for oxygen were substantially constant. A steel mill however usually has a. demand for oxygen that varies considerably at different times of the day and week. To provide such plant, which is large enough to supply oxygen at the peel; demand rate, involves not only high investment costs, but great inefiiciencies, it it is attempted to operate such plant at sub-normal rates; or it operated at a continuous full. rate; there is a serious problem of disposal of excess oxygen. By the principles of this inven tion such, problems are efficiently solved by providing a plant including a low-temperature air separation apparatus which islarge enough, to supply only the average oxygen demand, and also a store of liquid oxygen with means to vaporize portions thereof according to a variable demand in excess of the average. The stored oxygen consumed during peak demand periods can be replenished by liquid production during periods of below average demand. Further according to the invention, the stored liquid oxygen can be economically shipped to the plant from a large central plant because it is then practical to entirely eliminate the expense of providing mechanical refrigeration-producing devices, and the air separation apparatus will then be of a size suficient to produce oxygen from air and oxygen from the liquid used for refrigeration at. a rate to supply the normal constant oxygen demand, the peak demands being supplied by vaporization of portions of the shipped-in liquid oxygen.

Further objects of the present invention are: to provide a process of and apparatus for low-temperature separation of air by which an average or normal steady oxygen demand is supplied by separation of air by low-temperature rectification. and the excess demand peaks are supplied by vaporization of stored liquid oxygen; to provide an air separating plant. in which mechanical means to produce low-temperature refrigeration may be eliminated, the lowtemperature refrigeration requirement being supplied by vaporization. of liquid oxygen; and to provide a simple apparatus by which the refrigeration of liquid oxygen which isvaporized to supply part of a demand for gaseous oxygen is usefully employed for the refrigeration requirement of low-temperature separation of enough air to provide the balance of the demand for gaseous oxygen.

These and other objects and advantages of the inven- -tion will become apparent from the following description and the accompanying drawings showing exemplary em bodiments of apparatus for separating gas mixtures such as air, and including improvements according to the invention. In the drawing:

Fig. 1 is a schematic view of an exemplary air separat ing apparatus including mechanical refrigeration-producing means and, according to the invention, means to supply refrigeration from a stored body of liquid oxygen, and means to supply demand peaks by vaporization of stored. liquids; and

Pig. 2 is a schematic view of an air separation plant without mechanical refrigeration-producing devices and, according to the invention, including means for supplying the refrigeration from a stored body of liquefied gas such as liquid oxygen and means to supply demand peaks by vaporization of stored liquid.

in the drawings, similar items of apparatus in the figures are designated by the same reference characters.

Referring now to the drawings, and particularly to Fig; l, a means for preparing air for rectification which is intended to be representative of means customarily employed for such purposes, includes at 10 a compressor which preferably compresses the air to be separated to a pressure below p. s. i. (pounds per square inch).

3 Such air is cooled to substantially its condensation temperature by passage through alternately reversed pairs of regenerators 11 and 12, the pair of regenerators 11 being .cooled by outfiowing nitrogen product and the regenerators 12 eing cooled by outfiowing oxygen product. The air 13 conducted to the warm ends of the regenerators by a conduit 13 with branches 14 and 15. The branches 14 and 15 connect respectively to reversing valves 16 and 17 i at the warm ends respectively of regenerators 11 and 12. ets of automatic valves 18 and 1% at the cold ends of the regenerators 11 and 12 discharge the cooled air, which has been freed of moisture and carbon dioxide in the regenerators, to branch conduits 20 and 21 connecting to conduit 22 that discharges the air into the lower part of a scrubber separator 23. The scrubber separator 23 is a device for washing the incoming air with liquid air to scrub out residual hydrocarbon impurities and any particles of residual carbon dioxide The upper portion of the scrubber separator 23 eliminates entrained liquid particles and provides a clean vapor that is conducted by conduit 24 to the lower end of an air-separating rectifying column C.

The rectifying column C may be of customary construction, having a high pressure chamber 25 closed at its upper end by a. condenser 26. The condenser 26 operates n the customary manner to condenser vapors rising in the chamber 25, producing reflux for the chamber, and also producing liquid nitrogen that is collected on a shelf 27 directly under part of the condenser 26. The

a liquid nitrogen from the shelf 27 is conducted by a conduit 28 to the upper end of a low-pressure rectifying chamber 29 which is mounted above the chamber 25 and has at its lower end a liquid oxygen collecting space 30 that surrounds the condenser 26. hers may be provided with customary gas and liquid contact rectifying trays 31. i

In the scrubber 23 the scrubber linuid that collects impurities flows into a cup 33 from which it is discharged through a conduit 34 provided with an expansion valve 35. The conduit 34 conducts the li uid to a set of filters 36 and the cleaned scrubber liquid is conducted from the filters throu h a conduit 37 to an intermediate nortion of the low-pressure rectifying chamber 29. Liquid that collects in the lower uart of the hi hressure rectifying chamber 25 is conducted by a conduit 38 controlled by expansion valve 39 to the conduit 37 for delivery to the lntermediate part of the low-pressure chamber 29. The nitrogen product of rectification leaves the chamber 29 through a conduit 449 which preferably delivers the cold gaseous effluent to a heat exchanger 41. surrounding a heat exchange coil 42 which is interposed in the conduit 28 for sub-cooling the nitrogen reflux so as to avoid excessive vaporization when the reflux is expanded through an expansion valve 43 also inter osed in the conduit 23. From heat exchanger 41 a conduit 44 conducts the ciliaent nitrogen to heat exchange coil 45 located in the upper part of the scrubber separator 23, the purpose of the heat exchange coil 45 being to liquefy some of the scrubbed air to provide scrubber liquid. From coil 45 a conduit 46 conducts the cfiluent nitrogen to the reversing valve system 18 at the cold end of the re enerators 11. The warmed nitrogen leaves the reversing valve system 16 at the arm and of the regenerators through a conduit 47.

The oxygen product of rectification which boils in the space 3% produces cold gaseous oxygen that is conducted by a conduit 4-3 controlled by a valve 49 to a second heat exchange coil 5%? in the upper part of the scrubber cham- 1 her 23 and from coil 50, a conduit 51 conducts the product oxygen to the reversing valve system 19 at the cold end of the regenerators 12. The oxygen product is delivered from the warm end of the regenerators 12 through a conduit 52 controlled by the reversing valves 17.

The portions of the system described thus far do not provide enough refrigeration for operating the system,

- and therefore a means for producing the necessary low The rectifying chamtemperature refrigeration must be employed. An exemplary means is provided by an expansion turbine 54 which expands a portion of air from substantially the compression pressure to the pressure of the column 29. For such expansion, air free of carbon dioxide is preferred to avoid difficulty, sothat'a portion of the scrubbed air from the chamber 23 is employed. Such air, however, is already at condensation temperature, and it must be warmed to provide efiicient production of refrigeration by expansion with external work;

Such warming is preferably efiected by a portion of the incoming air in order to avoid loss of refrigeration. To this end there is drawn from an intermediate part of the regenerators through connections 55 controlled by valves 55' an equivalent portion of air which is conducted by a conduit 56 to the warm end of a heat exchanger passage 57. From the cold end of the passage 57 a conduit 58 conducts the cooled withdrawn portion of air to the lower part of the scrubber chamber 23. For use as explained hereinafter, a bypass 59 from conduit 56 to conduit 58 is provided and valves 60, 61, and 62 are interposed respectively in conduits 56, 53, and 59. The air to be expanded is taken from chamber 23 through a conduit 63 that conducts it to the cold end of a heat exchange passage 64 around the passage 57, and from the warm end of the heat exchange passage 64 a conduit 65 conducts the air to the inlet of the expansion turbine 54. A conduit 66 conducts the expanded air to an intermediate part of the chamber 29.

There is preferably provided a by-pass 67 between conduit 63 and conduit 65 controlled by a valve 69. The connections of conduits 63 and 65 with the heat exchange passage 64 are controlled by valves 71 and 72 respectively, and a valve 73 is interposed in the conduit 66. Valved connections 74 and 75 are disposed at the ends of the heat exchange passage 57 for use when thawing the passage of accumulated carbon dioxide. A normally closed by-pass 66' may be connected between conduits 66 and 44 for use when starting the plant.

Since only one heat exchanger 57 is provided, the turbine 54 is shut down when the heat exchanger 57 is taken out of service for thawing. Refrigeration for continuing the operation is provided, according to Fig. 1, by supplying liquid oxygen of the desired purity to the oxygen boiler space 30. Such liquid oxygen may be stored in a well-insulated storage tank 8% which is surrounded by an insulating jacket 81 providing one of the best insulations for the purpose, for example, a space filled with powder and highly evacuated of gas. The tank may be large enough to supply liquid for a period necessary to thaw out the heat exchanger 57. Preferably the tank 80 is much larger for purposes to be described hereinafter.

The oxygen is fed from tank 80 through a conduit 82 controlled by a valve 83 and connecting to the oxygen boiler space 30. A pipe 84 may also be provided connecting the upper parts of the space 30 and the tank 89 for equalizing of pressures and transmission of vapors from the tank to the space 30. During normal operation the tank 8!) may be gradually filled by drawing liquid oxygen from the space 30 through a conduit 85 connecting with the tank 80. If the tank 80 is mounted at the same level as the space 30, gravity flow could be relied upon for moving the liquid into the tank. If the tank 80 is positioned at a higher level, as indicated in Fig. 1, a liquid oxygen pump 86 may be interposed in the conduit 85. Since it may be desirable to add liquid oxygen to the tank 80 from an outside source, a normally closed supply connection 87 may also be provided. The tank 80 may also be provided with a suitable liquid level indicating device 88. All cold conduits and apparatus are protected by heat insulation according to the usual practice.

The product oxygen having a desired purity for consumpt on usually is desired at a higher'pressure than oneness available in conduit 52 and the conduit 52 therefore connects with the inlet of an oxygen compressor 90, the

discharge 91 of which connects to a pipe line 92 conducting the oxygen to the consuming apparatus which has a constant demand and periodic peak demands. The air separation apparatus may be of a size to produce gaseous oxygen and some liquid oxygen, at a total rate substantially equal to the mean or average consumption. The compressor 9% may be operated at a rate to compress the gaseous oxygen made at a rate equivalent to the steady consumption and when consumption is low, some liquid oxygen is pumped by the pump in; through conduit 85 to the storage vessel 80. For supplying the peak demands, a means for vaporizing portions of the stored liquid and feeding it to the pipe line is provided.

If the pipe line pressure is low, a gravity fed vaporizer could be used. Preferably the liquid is fed through a pipe 93 controlled by valve 94 to a pump 95, which may be similar to the pump described in U. S. Patent 2,455,460 to G. H. Zenner. From pump 95 the liquid may be fed through a suitable vaporizer 96 heated by a heating fluid and the resulting gas passed to the pipe line 92. A check valve 97 may be interposed in the connection 98 with the pipe line. The pipe line may have a pressure gauge 99 or pressure switch which will control the starting and stopping of the pump 95 according to the requirement for oxygen.

The operation of the system of Fig; l is believed clear from the above description. It is pointed out, however, that during steady operation, with the expansion turbine 54 in operation, the amount of refrigeration produced by the turbine is to be in excess of that required for operating the plant to produce the amount of gaseous oxygen product withdrawn through pipe 52. Such excess of refrigeration is provided so that the liquid which is to be accumulated in the storage tank 80 can be withdrawn from the boiler 36 at a slow rate by the pump 86. When the heat exchanger 57 is to be cut out of service for defrosting and the turbine 54 is to be shut down, operation of the plant and withdrawal from the system may continue by closing valves 66 61, 71, and 72 and opening valve 62 to by-pass the withdrawn air directly to the scrubber 23. Substantially all the scrubbed air then enters the lower column through conduit 24. When it is desired to maintain the turbine at operating temperature, a small flow of scrubbed air may be passed from conduit 63 by conduit 67 through the turbine to the upper column, by cracking valves 69 and 73. The heat exchange passage 57 is thawed by passing warm dry gas through it by use of the valved connections 74' and 75.

To prevent the lowering of the liqud levels in the rectifying column due to loss of refrigeration, liquid oxygen is drawn from the stored body in tank fill as needed. Such liquid oxygen may be fed to the liquid oxygen collecting space 3% at the needed rate regulated by the valve 83. As soon as heat exchanger 57 has been cleaned, it may be returned to service by opening valves so, 61, 71, 72, 73 and closing valves 62 and 69. When the turbine 54 is operating properly, the feeding of liquid oxygen to the chamber can be stopped by closing valve 83 and replenishment of liquefied oxygen begun by operation of pump 86.

if the refrigeration production of the expander 54 is not sufficient to provide enough liquid oxygen during the normal and below normal demands for ga s, there may be a gradual lowering of the mean liquid level in the tank 86 and then it will be preferable to ship liquid oxygen from a distant oxygen plant and add it to the tank 39 through connection 87. Usually it will be economical to provide the plant with a production capacity low enough so that the plant can operate continuously without accumulating more oxygen than can be used and if average consumption should be greater, to make up the difieren'ce by adding shipped-inliquid.

In the-plant of Fig. l the heat exchange between gas eons oxygen product and a portion of the compressed air is effected by regenerators l2 and the oxygen product purity will be less than 99%. Such oxygen is useful for metallurgical purposes. If a higher purity oxygen prodnot is required, the regenerator heat exchange system 12 is replaced by a set of counter-current heat exchangers that can be alternately defrosted or by other known sys tems such as non-reversed oxygen heating passages in the nitrogen regenerators or passage exchanging heat exchangers. The liquid oxygen. purity is preferably similar to the gaseous oxygen purity.

if the complete plant is shut down for a period, the re-starting of the plant can be facilitated by passing liquid oxygen from tank to the oxygen boiler Fit) to supplement the refrigeration produced by the turbine 54. After steady operation is attained the liquid oxygen store can be replenished. Also, if desired, liquid oxygen can be shipped to the plant and filled into tank 30 through the connection 87 before starting.

It is pointed out that according to-the invention several modes of operation may be practiced according to the service conditions. In one case the air supply and refrigeration-producing expander may be of a size to apply the gaseous oxygen for the constant demand by the pipe line and any demands for oxygen in excess of the constant demand would be supplied by vaporizing liquid oxygen from tank 80 which is replenished by liquid shipped from a distant plant.

A second mode of operation may provide the refrigeration machine only large enough to supply the low-temperature refrigeration for operation to supply gaseous oxygen for the low constant demand but air compression machinery, such as an auxiliary air compressor lit, and rent exchangers and rectifying columns of a size that can handle. some excess air so that when the oxygen demand is higher than the. low constant demand more air is compressed, cooled and fed to the column together with enough liquid oxygen from the storage tank 80 to pro vide the low-temperature refrigeration requirement over and above that which can be furnished by the expansion machine. The gas resulting from the liquid fed from tank 8%) combines with that resulting from air separation to furnish the gas demand by the pipe line. Sudden peak demands are supplied by vaporizing further portions of the shipped in liquid by operation of the pump 9'5 and vaporizer 96.

A third mode of operation is as previously described where the refrigeration machine and other air separation apparatus is of a size to produce oxygen in gaseous and liquid form to meet the total average demand, the liquid production during periods of low demand being used to replenish the store of liquid in tank 80, the periods of moderately high demand being met by increased air supply with increased gaseous oxygen production and reduced liquid production, the periods of peak demand being met by vaporizing some additional liquid from tank 89.

A fourth mode of operation contemplates the elimination of a specific mechanical refrigeration-producing de vice as in the embodiment illustrated in Fig. 2 wherein the low-temperature refrigeration needed for operation is obtained by the evaporation of liquid oxygen which may be shipped to the plant. Air is compresesd in the compressor 11th and passed to nitrogen regenerators ill through a conduit 113 in cooperation with reversing valves 116 and the cooled air is conducted from the regenerators through the medium of reversing valves H3 and a conduit 322 conducting it to the lower part of the scrubber chamber 123. From the top of the scrubber chamber 123 the air is conducted by conduit 124 to the lower part of the high-pressure rectifying chamber 11.25. The chamber 125 communicates with main condenser 126 in the lower part of the low-pressure rectifying chamber 129 and from a shelf 127 at the upper part of chamber 125 the transfer conduit 128 conducts liquid nitrogen to the top of the column 129. The scrubber liquid from the overflow cup 13?: in chamber 123 is conducted by conduit 134 and control valve 135 through filters 136 and through a conduit 137 to an intermediate part of the low-pressure column 129. A transfer conduit connection 138 conducts liquid from the bottom of chamber 125 to the transfer conduit 137 after throttling through a valve 139. Efiluent nitrogen flows from the top of the rectifying column through conduit 14% to a heat exchanger 141 in which is heat exchange coil 714-2 of the transfer conduit 12%, and from heat exchanger M2 a conduit 1e4- conducts the nitrogen to a heat exchange coil 145 in the upper part of the chamber 123, the nitrogen being then conducted from coil 145 through a conduit 146 to the regenerators 111 through the re ersing valves 118. The effluent nitrogen leaves the system through a conduit 147.

If it is desired to produce an oxygen product of, for example, not over 98% purity, a pair of oxygen regenerators could be used to recover the refrigeration of the product oxygen as, for example, shown in Fig. 1. However, if at least part of the oxygen demand is for high purity oxygen such as 99.5% purity, the warming of the oxygen product is eifected by indirect heat exchange, and to this end there is provided a series of heat exchangers comprising heat exchanger passages 150 pro vided in duplicate for receiving a portion of compressed air from conduit 113 through a conduit 151. From the cold end of the heat exchange passages 159 a conduit 152 conducts the partly-cooled air to another pair of heat exchange passages 153 in which the air may be partially liquefied. The thus cooled and partiallyliquefied air is conducted from the heat exchange passages 153 through a conduit 154 to a lower part of the scrubber chamber 123. The heat exchanges 150-153 are installed in duplicate so that one of a pair can be thawed out while the other is on stream so as not to interrupt operation. The product oxygen to be warmed is led by a conduit 3156 to the cold end of heat exchange passages 157 around passages 153 and from the Warm end of passages 157 through a conduit to the cold end of heat exchange passages 159 around passages 15%. The warmed oxygen is then conducted by a conduit 16% to the inlet of an oxygen compressor 161 which delivers it through a conduit 152 to a pipe line 163 leading to a consumer system including oxygen-consuming devices such as various operations in a large steel mill requiring high-purity oxygen.

The refrigeration necessary for continuing operation of the plant thus far described is provided by liquid oxygen which is fed from a storage tank 17th disposed within highly efiicient heat insulation t7 if this tank is situated at a proper elevation with respect to the rectifying column, the force of gravity may be relied upon for draining liquid at a desired rate from the bottom of the storage tank 175 through a conduit 172 to the oxygen boiling chamber 1319. Alternatively the liquid oxygen in the tank 170 may be stored therein under a pressure slightly higher than the pressure existing in the low pressure rectifying chamber 129, in which case the oxygen feed may be forced by pressure dilference to flow from the tank li tito the chamber 130. As another alternative, illustrated herein, a liquid oxygen pump 173 may be interposed in the conduit 172 so that the tank 179 may be at a low level and operated under atmospheric pressure, the liquid feed being forced by the pump from the tank 170 into the chamber 134). in any event, a control valve 174 is interposed in the conduit 172. The tank 179 may be filled from time to time through a filling connection 175, and vapors produced by heat leak to the stored liquid may be transferred from the upper part of the tank 170 through a conduit 176 to the suction side of the oxygen compressor 161.

When the pipe line demand is variable, the plant is economically constructed and operated to produce oxygen corresponding to the low constant demand rate, and for supplying the excess peaks of demand there is conveniently provided a vaporizer 1'78 interposed in a conduit 179 connected between the discharge side of a pump 18% and the pipe line 163. The suction side of the pump 849 is connected by a valved conduit 181 with the bottom of the storage tank 176*. If a quantity of lower-purity (for example, oxygen is also required, such purity oxygen can conveniently be provided and supplied to a pipe line 182; by admixing a portion of compressed air with a portion of the high-purity oxygen delivered through the conduit 169, the connections for such purpose being controlled by valves 133 and 184 respectively.

The suction of the compressor 161 may communicate with a pressure responsive device 187 to control the operation of the compressor so that a constant low pressure is maintained in pipe tea. The pipe 179 may be controlled by a check valve 136 allowing flow only toward the pipe line 163 and may communicate with a pressure responsive device 18% that controls the operation of pump 18th to maintain the pressure in the pipe line within desired limits.

in the operation of the plant it may be desirable to have the air supplied through the heat exchangers 156 and 153 at a slightly higher pressure than that which is supplied through the regenerators ill and therefore there maybe interposed in the conduit 151 a booster compressor 185. The amount of air compressed, cooled and fed to the rectification can also be varied within relatively narrow limits, the liquid oxygen feed being adjusted accordingly.

In the operation of the embodiment of Fig. 2, all the oxygen shipped to the plant in liquid form and periodically filled into the tank 170 is used to furnish gaseous oxygen to the consumer pipelines. A larger amount of oxygen, however, can be produced by operation of the air separation plant than the amount of oxygen produced by vaporizing the liquid oxygen fed to the chamber from tank 17%. At the same time the refrigeration of the liquid oxygen fed to the chamber 139 is usefully employed. It is seen therefore that the system economically supplies a large amount of gaseous oxygen at or close to the place of consumption while requiring the shipment of only moderate amounts of liquid oxygen from a distant liquid oxygen plant. The investment expense as well as the maintenance expense of a refrigeration turbine and large heat exchanger are likewise saved. The system is capable of supplying a variable demand with a low investment and operating expense.

In the operation of a system according to Fig. 1 it may be desirable to provide an air expansion device such as the turbine 54 of a type which can be regulated to efliciently expand a larger or smaller proportion of the air supply and with such an expander a mode of operation according to the invention would provide a constant air supply from compressor 10, and, when the consumer systern demand is low, diverting a larger proportion of the air through the expander to increase the refrigeration production so that a larger proportion of the oxygen product is made as liquid withdrawn by pump 86 and passed to storage 80 and the proportion of production as gas may be low. As the demand increases, the proportion of air expanded is to be decreased for making relatively less liquid oxygen and more gaseous oxygen until the amount of refrigeration is reduced to that required for making no liquid oxygen, the production then being all as gas. For further increase of demand, portions of stored liquid are withdrawn and vaporized as previously described.

This application is a continuation-in-part of my copending application Serial No. 120,788 filed October 11, 1949 now Patent No. 2,664,718.

it will be understood that modifications of the systems disclosed herein may be made without departing from the principles of the invention:

avenues What is claimed is:

1. In a process for supplyingoxygento consumer system having a variable demand for same including periods of normal demand and of demand in excess-of the normal and including the low-temperature separation of air by rectification in which air cooied and freed of moisture and carbon dioxide is subjected to low-temperature rectification to separate oxygen and nitrogen rich products, which products are used to cool further portions of air, the steps of providing astore of liquid comprising mainly oxygen; holding said store of liquid separate from the liquids involved in the rectification; during continuous rectifying operation, utilizing portions of said store of liquid to produce refrigeration for the rectification at a rate sufiicient to provide the low-temperature refrigeration requirements of the air separation in excess of that gained by pretreatment of the air including said cooling of air by the products; delivering. the oxygen product of the air separation and oxygen product resulting from the liquid drawn from said store of liquid to the consumer system during periods of normal demand; and withdrawing, gasifying, and deliveringadditional oxygen-from said store of liquid to the'consumer system-in accordance with the demands in excess of normal.

2. A process for supplying oxygen to a consumer system having a variable demand according to claim 1 in which the rate of air supply for the air separation and the rate of feed of liquid from said store of liquidtothe air separation are correspondingly varied according to variations of demand for oxygen by the consumer system.

3. A process for supplying. oxygen to a consumer system having a normal oxygen demand, periods of low demand and periods of demand in excess of the normal andincluding the low-temperature separation of. air by rectification in which air cooled and freed of moisture and carbon dioxide is subjected to low-temperature rectification to separate oxygen and nitrogen rich products, which products are used to cool further portions of air, the steps of providing a store of liquid comprising mainly oxygen; holding said store of liquid separate from the liquids involved in the rectification; during continuous rectifying operation, utilizing portions of said store of liquid to produce refrigeration for the rectification at a rate sufficient to provide the low-temperature refrigeration requirements of the air separation in excess of that gained by pretreatment of the air including said cooling of air by the products; delivering the oxygen product of the air separation and an: oxygen product resulting from the liquid drawn from said store ofliquid to the consumer system; said refrigeration gained by pretreatment of the air including the cooling of the air by the products providing for continuous separation of enough air to produce gaseous and liquid oxygen the total of which is equal to an average demand by the consumer; feeding. the liquid oxygen produced to said store of liquid during periods of low demand, the gaseous oxygen product being delivered to the consumer; and feeding additional cooled air to the air separation during periods of greater demand to produce proportionately more gaseous and less liquid oxygen.

4. A process for supplying oxygen to a consumer system having a variable demand for same comprising effecting the low-temperature separation of air which has been cooled and freed of moisture and carbon dioxide by subjecting it to a low-temperature rectification producing oxygen and nitrogen rich products; using such products to cool further portions of air; providing a store of liquid comprising mainly oxygen received from a source other than said rectification; holding said store of liquid oxygen separate from the liquids involved in the rectification; providing substantially all the low-temperature refrigeration needed in the air separation over and above that regained by pretreatment of the air including said cooling of air by said products during operation by feeding portions of liquid from said store to the rectification, the oxygen product corresponding to such portions of liquid being: delivered .to the consumer system with. the oxygen product of the air separationto supply a desired demand of the consumer; and during excess demand periods, withdrawing, gasifying; and delivering additional oxygen from said store of. liquid to theconsumer.

5. A process for supplying oxygen. to a consumer system having a variable demand according to claim 4 in which the rate of air supply for the separation and the rate of feed of liquid from said store of liquid to the rectification are varied correspondingly according to moderate variations in demand by the consumer system.

6. The process for supplying oxygen to a consumer system having a variable demand for same comprising effecting the low-temperature separation separation. of air which has been cooled and freed of moisture and carbon dioxide by subjecting it to a low-temperature rectification producing oxygen and nitrogen rich. products; using such products to'cool further portions of air; pro viding a store of liquid comprising mainly oxygen; holding such store of liquid oxygen separate'from the liquids involved in the rectification; expanding with the production of external work a portion. of the air to provide substantially all the low-temperature refrigeration in. the air separation needed over and above that regained by pre treatment of the air including said cooling of air by said products during operation to supply a desired demand of a consumer; and during excess demandperiods, withdrawing, gasifying, and d'eliveringadditional oxygen from said store to the consumer system.

7. A process for supplyingoxygcnto a consumer system having a variable demand according to claim 6 in which the low-temperature refrigerationby external work is sufiicient to produce oxygenfrom. air separation. in both liquid and gaseous states; and during. periods of demand lower than the total: oxygen production, feeding liquid oxygen from the separation to said store of liquid.

8. A process for supplying. oxygen. to a consumer system having a variable demand according to claim 6 in which the low-temperature refrigeration by external work is sufiicient to produceoxygen. from air separation in both liquid and gaseous states in total amount equivalent to the average demand; during periods of low demand, feeding liquid oxygen from the separation. to said store of. liquid, and during. periods of. intermediate demand increasing the air supply to the rectification to produce proportionately more gaseous oxygen and less liquid oxygen.

9. A process for supplying oxygen to a. consumer system having a variable demand. for same comprising effecting the low-temperature separation of air which has been. cooled and freed ofmoisture and carbon dioxide by subjecting it to a rectification producing oxygen and nitrogen rich components; using such products to cool further portions of air; providinga. store of liquid comprising. mainly oxygen; holding some store of liquid oxygen separate from the liquids involved in. the rectification; providing low-temperature refrigeration in the air separation sufficient for the refrigeration requirements over that regained by the cooling of air by said products during operation to supply a desired demand of the consumer; part of said low-temperature refrigeration being provided by expanding with external work a portion of the air; the balance of said low-temperature refrigeration being substantially provided by feeding portions of liquid from said store of liquid to the rectification, the oxygen product corresponding to such portions of liquid being delivered to the consumer system with the oxygen product of the air separation; and during excess demand periods withdrawing, gasifying, and delivering additional oxygen from said store to the consumer system.

10. Process for supplying oxygen to a consumer system having a variable demand for same comprising separating air by low-temperature rectification to provide a gaseous oxygen product; continuously Compressing and delivering such product to a consumer system at superatmospheric pressure; providing a store of liquid oxygen arrears 11 of similar purity to that of the product of air separation; and, when the demand of the consumer systemcxceeds the amount of the oxygen product delivered, pumping portions of the store to said superatmospheric pressure, vaporizing the pumped portions, and delivering the resulting gaseous oxygen to the consumer system in accordance with the excess demand.

11. Apparatus for the low-temperature separation of air by rectification in a rectifying column having an oxygen rich liquid reboiler, pretreating means including airproduct heat exchange means for cooling the air to be rectified, said pretreating means providing part of the refrigeration required for said rectification; an insulated container for holding a substantial body of liquid oxygen separate from said column; means for supplying liquid oxygen to said container from a source other than said column; means for controllably feeding liquid oxygen from said container to said reboiler at a rate sufficient to provide the remainder of refrigeration required for the rectification which exceeds that regained from pretreatment of the air including said'heat exchange with the products of rectification; and means for delivering the oxygen product of the separation and oxygen vapor resulting from vaporizing the liquid fed to the rcboiler to consuming means.

12. Apparatus according to claim 11. which includes means for independently withdrawing from said container and vaporizing liquid oxygen to supply peak demands of the consuming means.

13. Apparatus for supplying oxygen to a consumer systern having a variable demand for same comprising the combination with apparatus for the low-temperature separation of air by rectification including a rectifying column having an oxygen-rich liquid reboiler, of an insulated storage container separate from such column for holding a storage body of liquid oxygen; means connected between said rectifying column and said storage container for controllably feeding portions of liquid from the container to the column; means for delivering an oxygen product from said air-separation apparatus to the consumer system; means connected to said storage container and said consumer system including a vaporizer for withdrawing portions of liquid oxygen, vaporizing same and delivering the resultant gas to the consumer system; and means for controlling such withdrawal according to a higher demand than is supplied by the delivery from the air separation.

14. Apparatus for supplying oxygen to a consumer system according to claim 13 which includes means connected between said oxygen-rich liquid reboiler and said storage container for feeding a portion of the liquid oxygen product in the liquid state to said storage container, and in which the air separation apparatus includes a means for producing low-temperature refrigeration to supplement refrigeration recovered by cooling air with the separation products.

. 12 15. Apparatus for supplying oxygen to a'consumer systern according to claim 13 in which said storage container -is also provided with a filling connection adaptedfor charging liquid oxygen into the container from liquid partly liquefied, and subjected to rectification producing oxygen and nitrogen rich products; using such products to cool further portions of air; providing a storage body of liquid oxygen of a purity equivalent to that of the oxygen supplied to the consumer system, holding such body of liquid separate from the liquids involved in the rectification; providing low-temperature refrigeration in the air separation by expansion with external work of a portion of the air; during periods of demand lower than the total oxygen production, increasing the proportion of air expanded to increase the proportion of oxygen production in the liquid state; feeding the liquid product to the storage body while passing the gas production to the consumer system; and when the demand increases, reducing the proportion of air expanded to reduce the proportion of oxygen production in the liquid state and increase the gas production. 7

17. In a process for the low-temperature separation of air by rectification in which air cooled and freed of moisture and carbon dioxide is rectified, subjected to a low-temperature rectification to separate oxygen and nitrogen rich products, which products are used to cool further portions of air, the steps of providing a store of liquid comprising mainly oxygen received from a source other than said rectification; holding said store of liquid oxygen separate from the liquids involved in the rectification; expanding with production of external work at least a portion of the air to provide low-temperature refrigeration to the rectification; utilizing portions of said store of liquid to provide the low-temperature refrigeration requirement of the rectification over and above that furnished by said expansion; and deliverinng the oxygen product of the air separation and an oxygen product resulting from the use of said portions of liquid from said storage body to the consumer system.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A PROCESS FOR SUPPLYING OXYGEN TO A CONSUMER SYSTEM HAVING A VARIABLE DEMAND FOR SAME INCLUDING PERIODS OF NORMAL DEMAND AND OF DEMAND IN EXCESS OF THE NORMAL AND INCLUDING THE LOW-TEMPERATURE SEPARATION OF AIR BY RECTIFICATION IN WHICH AIR COOLED AND FREED OF MOISTURE AND CARBON DIOXIDE IS SUBJECTED TO LOW-TEMPERATURE RECTIFICATION TO SEPARATE OXYGEN AND NITROGEN RICH PRODUCTS, WHICH PRODUCTS ARE USED TO COOL FURTHER PORTIONS OF AIR, THE STEPS OF PROVIDING A STORE OF LIQUID COMPRISING MAINLY OXYGEN; HOLDING SAID STORE OF LIQUID SEPARATE FROM THE LIQUIDS INVOLVED IN THE RECTIFICATION; DURING CONTINUOUS RECTIFYING OPERATION, UTILIZING PORTIONS OF SAID STORE OF LIQUID TO PRODUCE REFRIGERATION FOR THE RECTIFICATION AT A RATE SUFFICIENT TO PROVIDE THE LOW-TEMPERATURE REFRIGERATION REQUIREMENTS OF THE AIR SEPARATION IN EXCESS OF THAT GAINED 